Method of compounding rubber



l atented Nov. 10, 1931 TUNITED srArEs PATENT-OFFICE ILLIAM s. oALoorrAND WILL-mm arouemss, or PENNS GROVE, NEW JERSEY, AS-

sronons' T E. I. no PONT nn NEMOUBS & company, or WILMINGTON, DELAWARE,

. A CORPORATION OF DELAWARE METHOD or ,oo wroumime RUBBER No Draw ing.Application filed. June 13,

f This invention relates to a method'of treating rubber and theresulting rubber product "and more particularly concerned With a methodof treatment whereby 'a rubber'prodi not is'obtained which isunusuallyresistant'to deterioration and oxidation.

It is generally accepted that the rate of dedepending on various factorssuch as the com- I position of the stock, the form of the article andthe conditions under which it is used. Various materials have heretoforebeen in corporated in rubber stocks to inhibit deterioration.However,{most of the agents heretofore employed for this purpose havebeen open to the objection that they discolor the rubber. For somepurposes, such as white and light colored stocks it is essential thatthe rubber composition contain nothing which will cause discoloration ofthe cured stock even after exposure to direct sunlight.

The use of certain phenolic compounds to. retard the deterioration ofrubber has been suggested as, for example, in BritishcPatents #181,365and #142,083. In general, however, the phenolic compounds mentioned havea very great retarding effect upon vulcanization when the vulcanizationis carried out in l a press. For example, Pelizzola. (Giorn. 80 Chem.Ind. Applicata 6,. (1924) 5960) found that the addition of 1 part ofpyrogal- 101 to a mixture of 100 parts of rubber and 8- parts of sulfurincreased the time required for vulcanization from 2 hours to, 4 hoursat.

85 ,144 C, We have found that phenol, resorcinol-, and hydroquinone alsoexert this eifect WVith these objectsin view, wehave discow ered thatcompounds having the general formula 1929. Serial No. 370,735.

wherein R and R represent aryl or alkyl aryl 3 hydrocarbon radicals, thearyl nuclei of which are directly connected by a single bond, may beadded to a rubber mix without affecting the rate of cure. The resultingrubher when vulcanized exhibits a greatly, in-

p creased resistance to deterioration as comterioration of rubberarticles differs greatly I pared to rubber which contains noantioxidant. Moreover, when-so incorporated, these 'materials cause nosubstantial discoloration even upon exposure to direct sunlight.

In'order to disclose the invention in detail,

, the following examples of actual embodi- 7 7 Example 1Para-hydroxy-diphenyl,

is a typical example of the above described 1 type of compound and itsuse as an antioxidant is illustrated. below.

Two stocks were made up of the following composition; the proportionsgiven are by weight.

. Stock A Stock B Smoked sheets 100 Sulfur 2. 75 Z110 18.15Diorthotolylguamdme O, 5625 p-hydroxy-diphenyl 1. 0

j The tWo stocks were then cured under 40 lbsiof steam for 80 minutes.The cured samples were thereupon aged in an oxygen bomb at 7 0 C. under300 lbs. of oxygen. The time required for complete deterioration of thetwo stocks is indicatedbe'low:

Days For stock A 5 For stock B 12 It will be noted that the resistanceto deterioration of the stock containing the anticontrol.

oxidant was 1i0% greater than that of the stock containing noantioxidant.

The amount of discoloration was determined by exposure to theFade-ometer, sun

ence of p-hydroxy-diphenyl caused no greater discoloration than E mample2 The eii'eot on color of antioxidants of this type was also tested inthe followingstockof better light stability: l

. Titanox is a pigment containing approxi- I mately 7 5% barium sulfateand titanium oxide. (Gardner, Chemical Synonyms and -Trade Names, p.250.)

The two stocks were cured showed no greater discoloration than the control stock A. a

- It is often advantageous to treat vulcanpounds disclosedhereinabove isparticularly.

useful for this purpose. In general, the

antioxidant is dissolved in a solvent and the cured stock isthenimmersed in the solution. After suiiicient, time has elapsed topermit the desired degree of absorption, the solvent is removed in anevacuated desiccator. An

- example of this modification ofthe process follows. 7

Example 5 glycol-monomethyl-ether and 12.8 parts of benzene. Vulcanizedrubber prepared by. curln g the stock of the followlng compositlonSmoked sheets -i 100 Zinc oxide 18.15 Sulfur 2. v7 5Diort-hotolylguanidine For purposes of comparison, a strip of the samestock was immersed in ordinary commercial benzene and another strip-wasleft untreated.

, a complete deterioration is given below: under glass, and directly tosun. Thfepresthat observed in the" C C at 20' lbs. steam ,i .7 Ipressure for 20 minutes. Tests for discolora- 1 tion as indicated inExample 1 disclosedthat the stock 13 containing the antioxidant para-beta-naphthyl-phenol The three samples of rubber were then aged inan oxygen bomb at C. under 300 lbs, of oxygen pressure. The timerequired for 7 Days Control untreated (3 Benzene treated 7 Treated withpara-hydroxy-diphenyl solution 21 It will be noted that the resistanceto deterioration of the stock treated with a s0- lutionof theantioxidant is more than 200% above that of the untreated stocks.

Among other members of the'new group- ,7 of antioxidants in which R andR are aryl groups, Y 'is' 'hydrogen and the aryl nuclei are directlyconnected bya single bond, the following. compounds have been actuallytested -and found to have antioxidant prop; of pa-ra-hydroxyerties'comparable to those diphenyl.

OH Y ortho-hydroxy-diphenyl 7 para-a1pha-naplithyl-pbenol 4-11 drox-4'-methy1-diphenyl OH Y Y compounds are listed merely by way ofillusjtrationr It is'obvious that the two aryl A solution containing6.4% of para-hy droxy-diphenyl was made by dissolving 1. part by weightof the antioxidant in a mix-' ture of 1.9 parts by weight of ethylene-'groups may be connectedin various positions and that the hydroxy groupmay be attached 'to its aryl nucleus 1n various positions with suchas,ffor example,- alkyl groups, which groups would have very littleeffect upon the 5 properties of the particularcompound.

The antioxidants may be incorporated 0- 5625 "int0 'therubber by anywell known means,

for 40 minutes at 40 lbs. steam pressure was such as milling them intothe stock upon the rolls of an ordinary mill. Moreover, they may beemployed in various rubber compounds and' rubber substitutes suchas,'for

example, gutta-percha, balata, and synthetic rubber, and it is thereforeto be understood th'at'theinvention'is not limited to any particularrubber stock or rubber compound.

Also, the proprtions of the antioxidant em ployed may bevari d withinwide limits a1- Ill;

though under ordinary circumstances about 1% of the antioxidant based onthe weight of the stock treated has been found to be high- 1ysatisfactory.

As many apparent and widely different embodiments of this invention maybe made without departing from the spirit thereof, it is to beunderstood that we do not limit ourselves to the foregoing examples. ordescription except as indicated in the following claims.

lVe claim:

1. A. process of increasing the resistance of rubber to deteriorationdue to aging which comprisesthe step of incorporating with the rubber amonohydroxy antioxidant having the general formula wherein R and Rrepresent aryl radicals.

2. A process of increasing the resistance of rubber to deterioration dueto aging which comprises the step of incorporating with the rubber anantioxidant having the general formula 'HORR wherein R and R representaryl radicals, at least one of which represents a phenyl radical.

3. A process of increasing the resistance of rubber to deterioration dueto aging which comprises the step of incorporating with the rubber anantioxidant having the general formula 4:. In the preparation ofvulcanized rubber, the steps of incorporating with the rubber, prior tovulcanization, a vulcanizing agent and a monohydroxv antioxidant havingthe general formula (wherein R and R represent aryl radicals) andthereafter vulcanizing. I

5. In the preparation of vulcanized rubber, the stepsof incorporatingwith the rubber, prior to vulcanization, a vulcanizing agent and anantioxidant having the general formula oxidant of the type set forth inclaim 2 and thereafter vulcanizing.

10. A vulcanized rubber article obtained y with the rubber mix andthereafter vulcanizmg. 7

11. A process of increasing the resistance of rubber to deteriorationdue to aging, which comprises the step of incorporating with the rubberpara-beta-naphthyl phenol.

12. A process of increasing the resistance of rubber to deteriorationdue to aging, which comprises the step of incorporating with the rubber4-hydroxy-4-methyl diphenyl.

18. A vulcanized rubber article obtained by incorporatingpara-beta-naphthyl phenol with the rubber mix and thereafter vulcanizmg.

14. A vulcanized rubber article obtained by incorporating4-hydroxy-4-methyl di phenyl with the rubber mix and thereaftervulcanizing. i

In testimony whereof we affix our signatures. r I

WILLIAM S. GALCOTT. WILLIAM A. DOUGLASS.

vulcanization, an antioxidant of the type set forth inclaim 1 andthereafter vulcanizing. 9. A vulcanized rubber article obtained byincorporating with the rubber mix, an antiincorporatingpara-hydroxy-diphenyl.

